Discharge ratings for control structures at McHenry Dam on the Fox River, Illinois

Abstract

Twenty-three measurements of discharge were used to determine discharge ratings for the five adjustable sluice gates, spillway, and fish ladder at McHenry Dam on the Fox River in Illinois. Discharge ratings were determined for free weir, free orifice, and submerged orifice flow regimes. Hydraulic conditions that identify flow regimes at McHenry Dam are defined by ratios between headwater depth (h 1), tailwater depth (h 3), and gate opening (h_). Flow under the sluice gates is identified as weir flow when the ratio of gate opening to headwater depth is greater than 0.73, and as orifice flow when ha/h« is less than 0.73. Free orifice flow occurs when the ratio of tailwater depth to gate opening is less than 1.3, and submerged orifice flow occurs when h3/h is greater than 1.3. Flow under the sluice gates is identified as free weir flow when the ratio of tailwater depth to headwater depth is less than 0.75, and as submerged weir flow when h3 /h-| is greater than 0.75. Flow over the spillway is identified as free weir flow when the ratio of tailwater depth to headwater depth is less than 0.60, and as submerged weir flow when h3 /h 1 is greater than 0.60. Discharge coefficients to be used in equations to compute discharge for various hydraulic conditions were determined. Four discharge measurements, ranging from 169 to 2,990 cubic feet per second, were used to define discharge coefficients that varied from 2.61 to 3.14 for free weir flow over the spillway, Nineteen discharge measurements, ranging from 180 to 4,050 cubic feet per second, were used to define discharge coefficients for free weir, free orifice, and submerged orifice flow under the sluice gates. The average value of the discharge coefficient for free weir flow under the sluice gates is 3.17. Discharge coefficients for free orifice flow varied from 0.48 to 0.66 and the discharge coefficients for submerged orifice flow from the two measurements were 0.59 and 0.67.